Immunocytological Comparison of Native and Wound Periderm Maturation in Potato Tuber

American Journal of Potato Research, Mar/Apr 2004 by Sabba, Robert P, Lulai, Edward C

ABSTRACT

The maturation of potato (Solanum tuberosum L.) tuber native periderm and wound periderm, which develops to replace the native periderm when it is damaged, are agriculturally important processes that are poorly understood. While both types of periderm form from a phellogen layer that serves as a lateral meristem, there has been little research done on comparing the biochemical processes and steps involved in the maturation of the two types of periderm. Here, we use immunological techniques to compare some of the cell wall changes during wound and native periderm maturation. Consistent with our recent work on native periderm, we demonstrate that toluidine blue O is also useful for distinguishing between suberized and non-suberized cells in wound periderm. More importantly, we use the immunological probes JIM5 and JIM7 to show that there is no increase in either un-esterified or esterified homogalacturonan pectin epitopes in phellogen walls accompanying wound periderm maturation. In contrast, as we previously described, native periderm maturation and resistance to excoriation (skinning) is accompanied by an increase in relatively un-esterifled and esterified homogalacturonan pectin epitopes in the walls of phellogen cells. These results demonstrate that the biochemical processes responsible for maturation and resistance to excoriation differ between native and wound periderm. This dissimilarity between wound and native periderm maturation demonstrates the potential limitations in applying the wound periderm model to research on native periderm.

RESUMEN

La maduracion del peridermo native del tuberculo de papa (Solanum tuberosum L.) y del peridermo regenerado, el cual desarrolla para reemplazar al peridermo nativo cuando este sufre danos, es un proceso agronomicamente importante que es insuficientemente comprendido. Mientras ambos tipos de peridermo se forman a partir de una capa de felogeno que sirve como meristemo lateral, muy poca investigacion se ha hecho comparando los procesos bioquimicos involucrados en la maduracion de los dos tipos de peridermo. Aqui, usamos tecnicas inmunologicas para comparar algunos de los cambios en la pared celular durante la maduracion del peridermo nativo y del regenerado. Consistentemente con nuestro trabajo reciente sobre peridermo nativo, demostramos que el azul de toluidino O es tambien util para distinguir las celulas suberizadas y no suberizadas en el peridermo regenerado. Mas importante aun, hemos utilizado los probadores inmunologicos JIM5 y JIM7 para demostrar que no hay incremento de los epitopes de la pectina homogalacturona esterificada y no esteriflcada en las paredes de las celulas del felogeno. Estos resultados demuestran que los procesos bioquimicos responsables para la maduracion y resistencia a la excoriacion son diferentes para el peridermo nativo y para el peridermo regenerado. Esta disimilaridad entre la maduracion del peridermo nativo y la del regenerado demuestra las limitaciones potenciales que existen para aplicar el modelo del peridermo regenerado para investigar sobre el peridermo nativo.

Accepted for publication 25 November 2003.

ADDITIONAL KEY WORDS: cell wall, homogalacturonan, pectin, phellem, phelloderm, phellogen.

Mention of a trademark, proprietary product, or vendor does not constitute endorsement by the United States Department of Agriculture.

ABBREVIATIONS: BSA, bovine serum albumin; HG, homogalacturonan; PBS, phosphate-buffered saline; TBO, toluidine blue O.

INTRODUCTION

The potato periderm forms the primary protective barrier at the surface of the tuber. When the native periderm is damaged, a wound periderm forms internal to the damaged tissue. Both types of periderm form from periclinal divisions of a cork cambium or phellogen layer, which serves as a lateral meristem (Artschwager 1924; Peterson and Barker 1979). In native tuber periderm, the phellogen layer differentiates from the hypodermis early during development of the tuber (Artschwager 1924; Peterson and Barker 1979). Both the phelloderm and the phellem are derived from periclinal divisions of the phellogen, the phellem forming the protective suberized skin of the tuber (Lulai 2001). Immature native periderm is susceptible to skinning injury (excoriation), which leads to potato loses during storage. As the periderm matures, it becomes resistant to excoriation.

In the case of wound periderm, the phellogen layer develops amid parenchyma cells under the wound surface and becomes detectable after the closing layer begins to form (Thomson et al. 1995; Lulai 2001). As with native periderm, both wound phelloderm and phellem cell layers develop from the phellogen. The resulting wound periderm is located between the closing layer and the remainder of the tuber. Generally, the cellular outlines of wound periderm appear less organized than that of native periderm. As is the case with native periderm, an immature wound periderm is susceptible to excoriation. Excoriation of the wound periderm formed after a potato tuber is cut for seed can lead to infection of the seedpieces with decay organisms, and excoriation of the wound periderm formed before tubers are put into storage can lead to losses from dehydration, disease, and various defects.